The present invention relates to projection type display apparatus which projects an image onto a projection plane by use of a display element such as a liquid-crystal panel and an illumination optical system including a light source not using mercury, for example, a light emitting diode, a laser, and a phosphor, and in particular, to a technique to provide a projection type display apparatus including a combination of the projection type display apparatus and the illuminating optical system.
For example, for a projection type display apparatus for displaying on a projection plane, e.g., a screen or a board, a magnified image of a display screen of a display element configured by arranging therein a plurality of liquid-crystal panels and a plurality of small mirrors of reflection or transmission type, an illumination optical system of the display apparatus has been developed to obtain the magnified image with sufficient dimensions and brightness on the projection plane.
Particularly, in display apparatus employing a plurality of display elements, various illumination optical systems have been proposed to suppress deterioration in white balance of color images and to prevent color shading of color images. For example, according to a projection type display apparatus described in JP-A-10-171045, an illumination optical system of the projection type display apparatus includes a light source which is primarily an extra-high pressure mercury lamp having a high light emission efficiency per input power (70 lm/W). Also, in the development of illumination optical systems, to improve the light transmission ratio in a first array lens and a second array lens, it is highly desired to reduce distance between electrodes thereof.
Such extra-high pressure mercury lamp generates a large amount of ultraviolet rays and hence imposes stress onto organic substances such as a liquid-crystal light valve and a sheet polarizer included in an illumination optical system, resulting in short life of the mercury lamp. This possibly leads to a problem in which since the light transmission capability of the illuminating optical system is deteriorated due to wear of electrodes and opaqueness appearing in a light emitting tube, brightness of the mercury lamp is lowered in a short period of time.
To overcome this difficulty, research and development and various proposals have been made for projection type display apparatus employing solid light emitting elements such as red, green, blue light emitting diodes and organic electroluminescence (EL) elements. For example, JP-A-2004-341105 proposes a light source device including a solid light source, a phosphor layer to convert an ultraviolet ray emitted from the solid light source into visible light, and a transparent substrate.
Also, to solve the problem of JP-A-2004-341105, there has been proposed in, for example, JP-A-2009-277516 an optimal source device in which an excitation light radiated from a solid light source is emitted also as visible light with high efficiency.
In addition, for example, JP-A-2009-259583 proposes a light source of a projection type display apparatus including a combination of light sources utilizing different light emitting principles.
According to the technique described in JP-A-2004-341105, the light source device includes a solid light source, a phosphor layer to convert an ultraviolet ray emitted from the solid light source into visible light, and a transparent substrate. Since the technique employs an excitation light source in which an ultraviolet ray having high energy is used as the excitation light, optical elements onto which the ultraviolet ray is radiated are likely to be damaged. It is accordingly difficult to secure a long-term performance of the optical elements. To solve the problem, JP-A-2009-277516 has proposed a technique in which visible light having lower energy than the ultraviolet ray is radiated as the excitation light onto the phosphor.
On the other hand, for projection type display apparatus, JP-A-2009-259583 proposes a new light source combining a plurality of light sources of different light emission schemes. According to the proposal, the new light source includes a first light source which is a light emitting diode or a solid light emitting element to emit light with a predetermined wavelength, a second light source which is a light emitting diode or a solid light emitting element to emit excitation light, and a third light source which uses the excitation light from the second light source as excitation energy to emit light with a wavelength equal to that of the light from the first light source.
The conventional techniques disclosed in JP-A-2004-341105, JP-A-2009-277516, and JP-A-2009-259583 are techniques for the light sources, and consideration has not been given to matching of the light source with the illumination optical system of the projection type display apparatus employing a liquid-crystal display element. Hence, in spite of the long life of the light source itself, the long life cannot be necessarily guaranteed when it is employed as the light source of the projection type display apparatus.